Research objective: The development of temporal organization in voluntary behavior in normal and pathological populations is investigated using "nature's experiments" (sex differences, neurological instabilities, physiological determinants of physical growth, etc.) and "society's experiments" of social deprivation, as experimental variables. Our theoretical aim is to explore the role of rhythmical processes in central nervous system function in the temporal organization of sensory-motor and symbolic sequencing behavior. Our clinical aim is to investigate the relation between defects in temporal organization of voluntary behavior and academic performance, in children with learning disabilities and neuropsychological disturbances. Spatial abilities and sequencing skills are contrasted throughout as "psychologically opposite" parameters of cognitive style. Sex differences in develpmental differentiation are introduced to distinguish biological from experiential factors in the differentiation of spatial and temporal aptitudes. The relevance of sex differences for the significantly higher incidence of specific learning disabilities and academic failures among young boys than young girls is explored.